Download O`Brien et al. 1983. The cheetah is depauperate in genetic variation

Genetic diversity among populations
(and factors that increase or decrease diversity)
Populations that are spatially isolated will
tend to diverge genetically
• genetic drift
• natural selection and local adaptation
p = .5
q = .5
p = .7
q = .3
p = .55
q = .45
p = .5
q = .5
p = .8
q = .2
Genetic diversity among populations
• Increases due to isolation, followed by
– genetic drift
– inbreeding
– selection
– local adaptation
• Decreases due to gene flow (migration)
as migrants move between populations, they homogenize
allele frequencies among populations
• larger populations diverge slowly through drift
– few migrants needed to counteract
• small populations diverge rapidly through drift
– more migrants needed to counteract
Changes in genetic diversity among populations
m = proportion of population that migrates
Nm = number of migrants randomly exchanged per generation
Ne = 1,000, m = 0.01, Nm = 10
Ne = 100, m = 0.01, Nm = 1
approx 1 migrant/generation will maintain same alleles among
populations (= qualitative similarity)
but 10 migrants per generation may still permit significant
differences in allelic frequencies ( = quantitative dissimilarity)
Changes in genetic diversity among populations
m = proportion of population that migrates
Nm = number of migrants randomly exchanged per generation
Ne = 1,000, m = 0.01, Nm = 10
Ne = 100, m = 0.01, Nm = 1
“in the absence of natural selection, the amount of genetic
divergence among demes is a function of the absolute
number of migrants exchanged (Nm), not the proportion
of exchange (m)” (Allendorf 1983)
Isolation by distance
p = 0.55
q = 0.45
p = 0.65
q = 0.35
p=0.5
p = 0.5
q=0.5
q = 0.5
p = 0.4
q = 0.6
p = 0.75
q = 0.25
Isolation by distance
http://www.youtube.com/watch?v=31qBrRawDK8
Isolation by distance
Mussel ‘lures’ with glochidia
Genetic distance between populations
Elliptio dilatata
Clegg, S.M., S.M. Degnan, J. Kikkawa, et al. 2002. Genetic
consequences of sequential founder events by an island-colonizing
bird. PNAS 99:8127-8132
silvereye (Zosterops lateralis)
Issues with genetic diversity among populations
outbreeding depression/hybridization
• local adaptation
Issues with genetic diversity among populations
outbreeding depression/hybridization
• local adaptation
example: ibex extirpated from Czechoslovakia (Capra ibex ibex)
- transplanted from Austria successfully (Capra ibex ibex)
- then added bezoars (C. i. aegagrus) and Nubian ibex (C. i. nubiana)
- fertile hybrids rutted in early fall instead of winter (as natives did)
- kids of hybrids born in February, coldest
month of year, entire population
went extinct
David Hall
Issues with genetic diversity among populations
outbreeding depression/hybridization
• local adaptation
• co-adapted gene complexes
Loss of fitness due to Inbreeding:
accumulation of homozygous recessives
loss of superior heterozygotes
Outbreeding:
reduced fitness of F1 generation
- disruption of local adaptation
- epistatic interactions
reduced fitness of F2 generation
- breakup of co-adapted gene complexes
More empirical studies on inbreeding than outbreeding….
Reproductive success
inbreeding
depression
inbreeding
outbreeding
depression
random mating
inter-breeding
Why do we care?
Inbreeding: may be last recourse for endangered population
Outbreeding: dangerous consequence of saving small popns.
“Genetic pollution” controversy
Florida panther:
declined due to habitat loss, poaching, road kills
evidence of inbreeding:
low fertility, sperm abnormalities, cowlicks, kinked tails,
cardiac defects, undescended testicles, high disease rate
Florida panther:
Genetic studies indicated low variability:
Florida
Western US
Other felids
P
4.9
9.9
8-21
H
1.8
4.3
3-8
DNA H
10.4
29.7
45.9
Found to have hybridized with S. American subspecies; introgressed animals with higher P
Florida panther:
Outbred with sub-species from Texas - added 8 females in 1995
F1 hybrid kittens do not have cowlinks or kinked tails
Texas genes are now 15-29% of total
Cheetah (Acinonyx jubatus):
O’Brien et al. 1983. The cheetah is depauperate in genetic variation
- using protein electrophoresis
Species
Drosophila
Mus
Homo sapiens
Felis catus
Cheetah
#
popns.
N
43
>100
2
87
many >100
1
56
2
55
#
loci
24
46
104
55
47
% poly.
loci
43.1
20.5
31.7
22
0.0
av.
H
0.14
0.088
0.063
0.076
0.0
Cheetah (Acinonyx jubatus):
Menotti-Raymond and O’Brien et al. 1993.
- using protein electrophoresis, high-resolution PE, and mtDNA
Species
Drosophila
Mus
Homo sapiens
Felis catus
Cheetah
#
popns.
N
43
>100
2
87
many >100
1
56
2
55
#
loci
24
46
104
55
47
% poly.
loci
43.1
20.5
31.7
22
0.0
av.
H
0.14
0.088
0.063
0.076
0.0
Drosophila
Mus
Homo sapiens
Cheetah
1
1
1
1
20
54
72
many
155
11.1
4.1
1.2
3.2
0.04
0.02
0.063
0.013
Felis catus
1
17
46.0
Cheetah
3
76
45.0
34
6
O’Brien et al. 1983. The cheetah is depauperate in genetic variation
- assumed to be result of small N, bottleneck, then inbreeding
- highly vulnerable to disease outbreaks (50% mortality in one
captive population)
O’Brien et al. 1983. The cheetah is depauperate in genetic variation
- assumed to be result of small N, bottleneck, then inbreeding
- highly vulnerable to disease outbreaks (50% mortality in one
captive population)
Merola, 1994. A reassessment of homozygosity ….
- carnivores tend to show low levels of genetic variation
(several have lower levels of H and P than cheetah)
- measures of fluctuating asymmetry indicate cheetah is not
suffering from low homozygosity or genetic stress
- sperm deformities – do not affect fertility, may be normal in felids
- low litter sizes – in captivity (high in wild)
- susceptibility to disease – may be due to captive contact (in wild,
cheetahs avoid conspecifics)
Concluded that conservation is better directed at habitat